A medical device for treating cardiac arrhythmia is disclosed, including: a microprocessor (8) and a digital/analog module (9). A MCU (1) configures the medical device to operate in a modified DVI (R) mode in which: when receiving a signal indicating the sensing of an atrial event by a sense control/amplification unit (6), the MCU (1) sets a PANP interval and sends to a time control unit (2) a signal, controlling a first timing unit (11) to operate in a timing mode for a duration equal to a duration of the PANP interval; if a scheduled post-ventricular atrial escaping interval is to end at a time not within the PANP internal, the MCU (1) sends respective signals to a pacing control/generation unit (5) and the time control unit (2) to dictate the pacing control/generation unit (5) to deliver a pacing pulse and control a second timing unit (12) to use a PAVI as a next ventricular escape interval; and if the scheduled post-ventricular atrial escaping interval is to end within the PANP interval, the MCU (1) sends a signal to the time control unit (2), controlling the second timing unit (12) to use the PAVI as the next ventricular escape interval.